Axially Driven Piston-Cylinder Unit

ABSTRACT

An axially driven piston-cylinder unit comprising a cylinder, a piston that can be moved back and forth in the axial direction of the cylinder, between first and second piston positions, and a drive element that can be moved back and forth in the axial direction of the cylinder and is mechanically connected to the piston by means of a piston rod. The piston rod is connected to the piston or the drive element against the pretension of an elastic device, in such a way that it can be moved axially in relation to the piston or the drive element, such that when the piston head comes into contact with the front wall of the cylinder borehole, on the side of the cylinder head, the other movement of the drive element is performed against the force of the elastic device, thus braking the drive element.

The invention relates to an axially-driven piston-cylinder unit.

A piston-cylinder unit is known, for example, from U.S. Pat. No. 5,525,845. In that, the piston rod is rigidly joined, both to the axially-movable drive element of the linear drive and also to the piston. During operation of the piston, which is driven by the linear motor, a state can arise in which the axial oscillation of the unit comprising the movable drive element, piston rod and piston, experiences an increase in the amplitude of the oscillations, so that the piston head of the piston can strike against the top of the cylinder bore. This can result in damage to the piston head or the top end face wall of the cylinder bore.

The object of the present invention is to design a generic axially-driven piston-cylinder unit in such a way that the danger of damage to the piston or the cylinder is reduced.

This object is achieved by the features specified in the claims.

In normal operation of the piston-cylinder unit, the piston rod is exactly located, both on the piston and on the drive element, and no relative movement occurs between the drive element, piston rod and piston. Only in the case of an overload, when the force applied by the drive element exceeds the pretensioning force of the elastic device does a relative movement occur between the drive element and the piston rod or between the piston rod and the piston.

By the decoupling of the mass of the drive element from the piston, by means of the elastic device, the drive element is braked by the elastic device if the piston lands on the top end face wall of the cylinder bore during a movement of the piston into the compression position. By this means, only the mass of the piston, possibly including the mass of the piston rod but not including the mass of the drive element, will strike the top end face wall of the cylinder bore. The shock pulse which arises from this is significantly less, compared to a rigid unit comprising the piston, piston rod and drive element, so that the danger of damage to the piston head or the top end face wall of the cylinder bore, is also greatly reduced.

In an advantageous embodiment, the piston head is provided with an opening through which the first end of the piston rod is passed, such that the piston rod can move relative to the piston in the axial direction of the piston, where the elastic device is provided between the piston rod and the piston and whereby the elastic device pretensions the piston rod from the piston towards the driver device, where the piston rod is provided with an end-stop which prevents the piston rod from coming out of the opening. With this form of embodiment, the mass striking against the top end face wall is yet further reduced, because the mass of the piston rod is also decoupled from the piston.

It is particularly advantageous here if the passage of the piston rod through the opening is sealed, for which purpose a seal which encircles the piston rod is preferably provided. With this form of embodiment, the compression efficiency is improved, because the medium which is compressed by the piston cannot leak through the annular gap around the piston rod.

Another advantageous form of embodiment is distinguished by the fact that the drive element is provided with an opening through which the second end of the piston rod is passed, that the piston rod can move relative to the drive element, in the axial direction of the drive element, that the elastic device is provided between the piston rod and the drive element and that the elastic device pre-tensions the piston rod from the drive element towards the piston, where the piston rod is provided with an end-stop which prevents the piston rod from coming out of the opening. With this variant, the decoupling is effected by means of the elastic device on the drive element side, so that a fixed joint can be provided between the piston and the piston rod and it is not necessary to provide an expensive seal on an opening in the piston head.

Preferably, the elastic device will have a spring or will be made of a spring. Particularly preferred here is the provision of a disk-spring arrangement or a spiral spring under compression or tension.

A realization of the present invention is especially effective in the case of a linear drive, for example a linear motor, where the piston is subject to the back and forward drive of a movable drive element of the linear drive.

A preferred application of the axially driven piston-cylinder unit in accordance with the invention is its use in a compressor for producing a pressurized fluid.

The invention is explained in more detail below using an example, with reference to the drawing. In this

FIG. 1 shows a first form of embodiment of the invention with a decoupling mechanism in the region of the piston, and

FIG. 2 shows an enlarged diagram of the passage of the piston rod through the piston head, in the form of embodiment shown in FIG. 1.

FIG. 1 shows a longitudinal section through a piston-cylinder unit 1 with a cylinder 2 and a piston 3. The cylinder 2 has a cylinder bore 10, in which the piston 3 is accommodated so that it is freely guided and can move back and forth along the direction of the longitudinal axis X of the cylinder bore 10. The piston 3 has a gas bearing in the cylinder 2. The top end face wall 12 of the cylinder bore 10, formed in a cylinder head 23, the internal circumferential wall 14 of the cylinder bore 10 and the piston head 16 delimit the cylinder chamber 18.

An inlet manifold 22 with a valve 20, which is shown schematically, opens out into the top end face wall 12 of the cylinder bore 10. Also provided in the top end face wall 12 is an exhaust manifold 24, which has a corresponding valve 26; this exhaust manifold also opens out into the cylinder bore 10.

When the piston 3 makes a movement to the left in FIG. 1, fluid is drawn into the cylinder space 18 through the inlet manifold 22 and the inlet valve 20, and when the piston 3 makes a movement to the right this fluid is expelled in a compressed state through the exhaust valve 26 and the exhaust manifold 24. The piston-cylinder unit 1 shown is part of a piston-drive machine in which the expelled fluid is in gaseous form, such as is the case for a compressor, for example. However, the invention can in principle also be used with other piston-drive machines, such as for example pumps.

The piston 3 is driven by a drive element 50, of a linear drive 5 shown only schematically in the figure, which can execute oscillatory longitudinal movements back and forth along an axis Y. The movable drive element 50 is joined mechanically to the piston 3 by a piston rod 4. The piston rod 4 is inelastic in the axial direction, and is thus capable of transmitting axial forces from the drive element 50 to the piston 3.

The piston rod 4 is rigidly joined to the drive element 50. The piston rod 4 is guided in the piston 3 so as to be movable in the direction of the longitudinal axis X of the cylinder 2, or of the longitudinal axis X′ of the piston 3, which is coaxial with the former. For this purpose, the piston rod 4 has a bearing in an annular radial support 31 in the inside of the piston 3, where there is a fixed joint between the piston 3 and the radially outermost perimeter of the radial support 31, which has a central opening through which the piston rod 4 is guided so that it is movable.

A central through-hole 16′ is provided in the piston head 16, (FIG. 2), through which the first end 4′ of the piston rod 4, at the piston end, is passed in such a way that it can move axially. The face of the first end 4′ of the piston rod 4, at the piston end, is provided with a mushroom-shaped head 41, the domed surface of which faces towards the cylinder head 23. On the side which faces backwards towards the piston head 16, the mushroom-shaped head 41 forms an annular landing area 41′, the outer diameter of which is greater than the diameter of the opening 16′ in the piston head 16 so that the piston rod 4 is secured against slipping out, towards the left in the figures.

The first end 4′ of the piston rod 4, at the piston end, has a reduced diameter compared with the rest of the piston rod 4. Around this diameter can be arranged a seal 43 which seals the first end section 4′ of the piston rod 4, at the piston end, against the inner circumference 16′ of the piston head 16.

In the inside of the piston 3, in the region of the radial position support 31, an elastic device 6 is provided in the form of a domed annular disk-spring 44 with its outer perimeter fixed to the piston 3 and having a central hole through which the piston rod 4 is passed, where the inner circumference of the annular disk-spring 44 is fixed to the piston rod 4. In FIG. 1, the dome of the disk-spring 44 is convex towards the left, that is towards the drive element 50, so that the disk-spring 44 applies a pretension to the piston rod 4, towards the left in FIG. 1, as a result of which the annular surface 41′ of the mushroom-shaped head 41 on the first end 4′ of the piston rod 4, at the piston end, is brought into contact with the piston head 16 under the tension from the spring 44.

If the piston 3 is moved to the right in the figure, that is into the compression position in which the enclosed cylinder chamber 18 is minimal, then the piston head 16 moves to land on the top end face wall 12 of the cylinder head 23. Due to the mass inertia of the movable drive element 50 and piston rod 4, the drive element 50 and piston rod 4 continue their movement towards the right, against the force of the disk-spring 44, and are braked by the spring force of the disk-spring 44. When this happens, the mushroom-shaped head 41 on the end 4′ of the piston rod 4, at the piston end, lifts off from the piston head 16 and moves into a recess 25 which is formed in the cylinder head 23 in the region where the exhaust manifold 24 opens out into the cylinder chamber 18. In this way, the impact when the piston head 16 meets the top end face wall 12 is limited to the mass of the piston 3, while the masses of the drive element 50 and the piston rod 4 are braked by the spring 44, at a point in time after the piston head 16 hits the top end face wall 12.

Alternatively, the piston rod 4 can also have a fixed joint to the piston 3, with an axially movable bearing for the piston rod 4 being provided in the drive element 50, and the elastic element formed by the spring 44 being provided between the piston rod 4 and the drive element 50.

The invention is not restricted to the above exemplary embodiment, which is only for the purpose of explaining in general the core idea of the invention. Rather the device in accordance with the invention can, within the scope of the protection, assume other forms of embodiment than that described above. In this case the device can, in particular, have characteristics which represent a combination of the relevant individual characteristics of the claims.

The sole purpose of reference marks in the claims, in the description and in the drawings is to aid understanding of the invention, and they should not restrict the scope of the protection. 

1-7. (canceled)
 8. An axially driven piston-cylinder unit comprising: a cylinder having a cylinder bore with a top end face wall; a piston having a piston head and being movable back and forth along an axial direction of the cylinder between a first piston position, in which a cylinder chamber enclosed between the piston and the cylinder is largest, and a second piston position, in which the cylinder chamber is smallest; a drive element being movable back and forth along the axial direction of the cylinder; and a piston rod mechanically coupling the drive element and the piston and including a first end coupled to the piston and a second end coupled to the drive element; and an elastic device coupling the piston rod to at least one of the piston and the drive element with the piston rod being movable axially relative to at least one of the piston and the drive element respectively against a pretensioning force of the elastic device such that, when the piston moves into the second piston position at the top end face wall, the piston head lands on the top end face wall of the cylinder bore, then the further movement of the drive element is made against the force of the elastic device, and thus the drive element is braked.
 9. The axially driven piston-cylinder unit as claimed in claim 8, further comprising: an opening provided in the piston head and the first end of the piston rod extending through the opening; the piston rod being movable in relation to the piston in the axial direction of the piston; the elastic device coupling the piston rod and the piston; and the elastic device pretensioning the piston rod from the piston towards the drive device, the piston rod including a piston end-stop restricting the piston rod from coming out of the opening.
 10. The axially driven piston-cylinder unit as claimed in claim 9, wherein the piston rod has a sealed passage into the piston opening and a seal surrounding the piston rod.
 11. The axially driven piston-cylinder unit as claimed in claim 9, wherein the elastic device includes an annular spring disk.
 12. The axially driven piston-cylinder unit as claimed in claim 8, further comprising: an opening provided in the drive element and the second end of the piston rod extends through the opening; the piston rod being movable in relation to the drive element in the axial direction of the drive element; the drive elastic device coupling the piston rod and the drive element; and the drive elastic device pretensioning the piston rod from the drive element towards the piston, the piston rod including a drive end-stop restricing the piston rod from coming out of the drive opening.
 13. The axially driven piston-cylinder unit as claimed in claim 12, wherein the elastic device includes a spring.
 14. The axially driven piston-cylinder unit as claimed in claim 8, wherein the piston is subject to the back and forth drive from a movable drive element of a linear drive.
 15. A compressor for producing a pressurized fluid comprising: at least one axially driven piston-cylinder unit comprising: a cylinder having a cylinder bore with a top end face wall; a piston having a piston head and movable back and forth along an axial direction of the cylinder between a first piston position, in which a cylinder chamber enclosed between the piston and the cylinder is largest, and a second piston position, in which the cylinder chamber is smallest; a drive element being movable back and forth along the axial direction of the cylinder; and a piston rod mechanically coupling the drive element and the piston and including a first end coupled to the piston and a second end coupled to the drive element; and an elastic device coupling the piston rod to at least one of the piston and the drive element with the piston rod being movable axially relative to at least one of the piston and the drive element respectively against a pretensioning force of the elastic device such that, when the piston moves into the second piston position at the top end face wall, the piston head lands on the top end face wall of the cylinder bore, then the further movement of the drive element is made against the force of the elastic device, and thus the drive element is braked.
 16. The compressor as claimed in claim 15, further comprising: an opening provided in the piston head and the first end of the piston rod extending through the opening; the piston rod being movable in relation to the piston in the axial direction of the piston; the elastic device coupling the piston rod and the piston; and the elastic device pretensioning the piston rod from the piston towards the drive device, the piston rod including a piston end-stop restricting the piston rod from coming out of the opening.
 17. The compressor as claimed in claim 16, wherein the piston rod has a sealed passage into the piston opening and a seal surrounding the piston rod.
 18. The compressor as claimed in claim 16, wherein the elastic device includes an annular spring disk.
 19. The compressor as claimed in claim 15, further comprising: an opening provided in the drive element and the second end of the piston rod extends through the opening; the piston rod being movable in relation to the drive element in the axial direction of the drive element; the drive elastic device coupling the piston rod and the drive element; and the drive elastic device pretensioning the piston rod from the drive element towards the piston, the piston rod including a drive end-stop restricing the piston rod from coming out of the drive opening.
 20. The compressor as claimed in claim 19, wherein the elastic device includes a spring.
 21. The compressor as claimed in claim 15, wherein the piston is subject to the back and forth drive from a movable drive element of a linear drive. 